CODEWITHSUNDEEP
c#.netinterfaceicollection
Graham
Graham

Reputation: 1517

Casting ICollection of a concrete type to an ICollection of the concrete type interface

What is the recommended way to cast an ICollection<Bar> to ICollection<IBar> where Bar implements IBar?

Is it as simple as 

collection = new List<Bar>();
ICollection<IBar> = collection as ICollection<IBar>?

or is there a better way of doing it?

Upvotes: 4

Views: 5619

Answers (3)

Henrik
Henrik

Reputation: 23324

You cannot cast to ICollection<IBar>, but you can cast to IEnumerable<IBar>.

So if you don't intend to add something to the list, you can do this:

IEnumerable<IBar> enumeration = (IEnumerable<IBar>)collection;

The solutions from the other answers don't actually cast but create a new list that will not reflect subsequent changes to the original list.

Upvotes: 2

Tim Schmelter
Tim Schmelter

Reputation: 460208

You have to cast every item in the list and create a new one, for example with Cast:

ICollection<IBar> ibarColl = collection.Cast<IBar>().ToList();

In .NET 4, using the covariance of IEnumerable<T>:

ICollection<IBar> ibarColl = collection.ToList<IBar>();

or with List.ConvertAll:

ICollection<IBar> ibarColl = collection.ConvertAll(b => (IBar)b);

The latter might be a little bit more efficient since it knows the size beforehand.

Upvotes: 3

Matthias Burger
Matthias Burger

Reputation: 5946

Just convert all entries with

ICollection<IBar> ibars = collection.ConvertAll(bar => (IBar)bar);

I think this variant is also readable. Perhaps there are ways to cast it with more performance...

Upvotes: 0

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